Some former supporters of a mobile phone unlocking bill in the U.S. Congress have withdrawn their support for the legislation because of a new provision added to it as it heads to the House of Representatives floor for a vote.

A vote on the Unlocking Consumer Choice and Wireless Competition Act was scheduled for late Tuesday, but four lawmakers and digital rights groups Public Knowledge and the Electronic Frontier Foundation have withdrawn their support for the bill. Republicans managing the bill inserted language into the bill, after it was approved in the House Judiciary Committee, that would allow the continued prohibition of bulk unlocking of mobile phones for resale.

Unlocking a phone is typically used to switch carriers. In January 2013, the Library of Congress removed the act of unlocking a smartphone from the legal exceptions under the Digital Millennium Copyright Act (DMCA), and digital rights advocates have called on Congress to restore the protections.

The new wording favors mobile carriers, said Derek Khanna, a copyright reform activist. "Phone companies lobbied to make phone unlocking illegal, and now that the public has responded with outrage and demanded action the phone companies lobbyists have rewritten the legislation to go after their competitors," he said by email. "Many consumers have to rely upon others to unlock their devices for them; under this text small businesses could not provide that service."

Electronics resellers should be able to buy phones from consumers, and after ensuring they're not stolen, unlock them for resale, he said. "This is a critical part of how the wireless market functions," he added.

The bill, as written, would also allow the Library of Congress to again review the phone unlocking provisions in the DMCA in 2015, Khanna added. Congress should pass a permanent exemption, he said.

The new language in the Unlocking Consumer Choice Act weakens the bill, Representatives Zoe Lofgren and Anna Eshoo, both California Democrats, wrote in a letter to their colleagues this week. The change in the bill would give consumers less control over their mobile devices, and give companies more leverage to use the DMCA against them, they wrote.

"Congress should work to roll back abusive practices that use copyright law to prevent owners from having control over the devices they lawfully own," they wrote. "What it means to 'own' a device that has been purchased is what's at stake here. The new addition to the bill puts the effort to stand up for the property rights of the owners of technology devices at risk."

Lofgren was a sponsor of the bill. Also voicing opposition to the bill Tuesday were Representatives Thomas Massie, a Kentucky Republican, and Jared Polis, a Colorado Democrat.

The bill, sponsored by Representative Bob Goodlatte, a Virginia Republican, still has a good chance of passing through the House. The Senate would need to pass it, and President Barack Obama would need to sign it, before it became law. The bill still has several supporters from the Judiciary Committee.

The bulk unlocking provision addresses law enforcement concerns about the resale of stolen phones, a House staffer added.

In December, the five largest U.S. mobile carriers, under pressure from Congress and the U.S. Federal Communications Commission, announced plans to allow customers to unlock their mobile devices.

Grant Gross covers technology and telecom policy in the U.S. government for The IDG News Service. Follow Grant on Twitter at GrantGross. Grant's email address is grant_gross@idg.com.

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